I just purchased on '03 P71. It runs fine for the first 5 minutes when it's cold then it starts missing out and has no high rpm power even when cold. Also, it may be unrelated, but it has a belt squeeling type noise coming from the driver's side cylinder head area which we verified is nothing belt driven. So far this is what we have done: replaced the spark plugs (With OEM motorcraft), changed 3 ignition coils, fuel filter, swapped out the MAF sensor / IAT sensor. The codes in the computer are "Random Misfire" and also "Misfire Cylinder 5 & 7". It has previously thrown misfire codes for cylinders 4, 1, and 3 as well. My mechanic did a fuel pressure test, it was showing 30 psi constantly while driving on his gauge, but the computer was showing 41 psi (Spec is 30-45 I believe) I don't know if that makes sense or not. He used a smoke machine and did not detect any vacuum leaks. He did a compression test and all were fine except cylinder #7 was "A little low" I don't know how low or if he did a leakdown test. It does not lose a drop of oil or coolant and there is not smoke from the tailpipes (although I can smell unburnt exhaust sometimes at idle). The engine sounds normal with no noises other than that squeeling which is worst at around 1500 rpms. Anybody have any ideas? My mechanic and I are completely frustrated.

Have you tried to see which cyl. or cyls are missing by disconnecting the injectors one at a time to pinpoint the miss? The squealing noise could be the A/C compressor pulley or one of the idler pulleys. Take the belt off and run it to see if it goes away.

We unhooked the belt and it still squeels internally. The noise has almost gone away with some lucas oil stabilizer. My only concern now is the misfire. The odd thing is today we went for a drive with the diagnostic computer running, the car ran well for 4 miles, then started missing badly, the computer set 7 codes, they were "Cylinder X Circuit Malfunction" for every cylinder except #3. My mechanic has tested the wiring harness from the pcm to the COPs and was fine. The ignition coils and plugs are fine, the fuel injectors are fine, the engine grounds are fine. Another interesting point, at a stop light the computer was leaning out the fuel mixture to -0.0% and when we tried to leave the stop light, the car would not move at all and then as if a light switch had been flipped it ran flawlessly. The only other code which we have never gotten before was "Cylinder Head Temperature too low 53 degrees" which was after the engine was fully warmed up. Mechanic tested spark on all cylinders and it appeared to be random, we replaced the PCM with one from an 03 Grand Marquis and the spark was then constant, but the fuel pump would not run off of that computer. We are leaning towards the PCM being shot, although I think that's kind of rare. I've heard the PCM's interchange between 99 and 03, but the salvage yards swear up and down it has to be an 03 police car. Any other thoughts? Thanks for your help.

Thanks for the good ideas. The backpressure has been tested and is less than 1 psi per side on the exhaust. The computer from the 03 Grand Marquis made the ignition coil test light work perfectly whereas the original PCM did not. The only problem was it would not run the fuel pump (PATS security issue from the Grand Marquis???) Anyway, hopefully the computer is the problem, otherwise I am out of ideas, like I said he tested the circuits between the PCM harness and the ignition coils and it was perfect. I guess I did forget to mention how the check engine light on the car did not illuminate even though there were 7 ignition coil circuit fault codes in the computer. The check engine light does work when you turn the ignition on so I know the light isn't burnt out and it's lit up before and flashed a few times as well.

hi carproof i can understand exactly where your coming from because ive been stumped for months on what is wrong with my cv but anyway from what you explained it sounds like an exhaust problem and you said the fuel pressure was ok thats my second guess its very frustrating having a multiple misfire because theres soo many tests that you have to run before you get to the actual problem good luck let us know what you find out

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